U.S. Pat. No. 4,750,800 ('800) to Fournier et al., assigned to the assignee of the present invention, articulately presents an explanation of the background art involved in the mounting of integrated optics devices to substrate materials. Although a good approach, this attempt had several shortcomings.
'800 teaches an apparatus comprising a lithium niobate (LiNbO.sub.3) integrated optics (IO) chip mounted to a LiNbO.sub.3 substrate with an ultraviolet cured adhesive. The substrate is mounted to a support package structure with a compliant adhesive bonding. However the substrate must be at least ten times the thickness of the IO chip in order to reduce the thermally and G-shock induced stresses transmitted through the substrate from the support package.
This constraint presents a problem since LiNbO.sub.3 with a 10 millimeter(mm) thickness is not available as a stock size and therefore is more expensive to procure. In addition, if the thickness of the substrate is reduced, less volume is required for the packaging along with less weight for the system in which the IO chip operates.
One application for integrated optics chips is in fiber optic rotation sensors (e.g., a fiber optic gyro) which may be used to provide guidance for precision guided weapons and tactical missiles. In particular, fiber optic rotation sensors may be employed in smart artillery shells such as the proposed Advanced "Copperhead". Since this type of shell is launched from an artillery piece (e.g., a 155 millimeter howitzer), high G-shock loads occur when the shell is being fired. This type of launching places a great deal of shock on components within the shell and thus innovative packaging techniques must be used if active electronics are to be placed within the shell.
The active electronics envisioned operating within these shells must sustain 20,000 G shock loads. This requirement creates a tremendous problem to designers involved with fiber optic rotation sensors since the performance of the LiNbO.sub.3 IO chip is susceptible to stresses transmitted through the substrate. These stresses spuriously change the refractive index of the IO chip, thereby interfering with the modulation being performed in the IO chip as part of the well known signal processing in the rotation sensor. This interference results in an error in the detected rotation rate of the rotation sensor and hence reduced sensor performance and accuracy.